This invention relates to conversion of biomass, i.e., fibrous plant matter, carbon waste products and organic chemicals (including any toxic compounds such as chlorinated organics, PCBs, etc.) into synthesis gas (useful fuel gases; namely, hydrogen gas and carbon monoxide) and is more particularly concerned with an effective process for converting all plant matter as well as all dried organic material by contact with superheated steam (Flash Hydropyrolysis™).
Biomass is a term used to refer to any material of agricultural origin, and a number of candidate materials that are biomass based can be considered possible feedstock for different energy producing procedures. Some common processes for energy extraction have employed various forms of fibrous plant matter, such as wood chips, straw, hay, corn stalks, or similar agricultural by-products. Manure is sometimes used. It is expected that in future some varieties of plant will be grown and harvested expressly for energy production from the biomass they produce.
Although biomass has a complex composition, if can basically be considered as being composed of three major components, namely, cellulose, hemicellulose, and lignin. These three components together usually form up to about 90% of the dry weight of any biomass material. Dependent on the plant source, the balance is ash (5 to 10%) and small amounts of numerous minor organic materials such as proteins, tannins, essential oils, oils, waxes, pitch, etc.
If the energy of the biomass is extracted by direct burning, then the energy content varies depending on moisture content and other factors. The heat of combustion of a number of dry biomass sources is as follows (in units of Kcal/Kg):
Bagasse4596Buckwheat hulls4688Coconut shells4827Oak bark4862Wood:beech4793birch4784oak4586pine5022
The noticeably higher heat of combustion of pine wood is due to its high pitch content, with pitch, like lignin, being less oxygenated than cellulose or hemicellulose and therefor containing more available energy (more material available to be oxygenated). The heat of combustion of lignin alone is 5101 Kcal/KG, and that of pitch is 8400 Kcal/Kg. However, regardless of source, dry biomass contains at least about 4500 Kcal/Kg of available energy.
The direct burning of biomass has been an ineffective way of obtaining its energy. The biomass materials, e.g., hay, straw, leaves, seed hulls, etc., are complicated materials that release gases rather quickly during the burning process, but leave the carbon component (typically 70% to 80% by weight), which is difficult to burn. Therefore burning facilities have to be specifically designed and controlled to burn the carbon component and obtain high efficiency.
Biogas (mostly methane) can typically be obtained by the biological breakdown of biomass (i.e., fermentation) in the absence of oxygen. Any biological refuse, such as cattle and pig manure, green parts of plants, corn stalks, straw, hay, wood chips, saw dust, etc., can be used. The bacteria responsible for breakdown are usually mesophiles that grow optimally at temperatures of 37° C. to 43° C., and/or thermophiles that grow at temperatures between 50° C. and 60° C. This is a slow process, and therefore a processing plant needs to be quite large for economical operation. In addition, especially during the growing season, there is a problem with utilization of large amounts of co-produced heat.
Ethanol fermentation from biomass has been discussed as a way of obtaining a liquid, i.e., portable transportation fuel. The current technology for the fermentation of corn (maize) to produce ethanol typically involves fermentation of the edible portion of the plant exclusive of the residual biomass matter (ethanol biomass conversion processes are dependent on the use of simple, fermentable sugars—i.e., monosaccharides or disaccharides). Polymerized sugars like starch (polymeric glucose) or insulin (polymeric fructose) can be used for alcohol fermentation. only after they have been converted to simple saccharides by a process called saccharification. The simple sugars then are fermentable by yeast or certain bacteria. Because only the sweet or food parts of the plant are available, which constitute only a small portion of the plant, ethanol fermentation is not a particularly effective use of the biomass energy content. Furthermore, with existing ethanol technology, only about one-third of fermentable sugars are converted into ethanol. Also, it has been calculated that production of ethanol by fermentation requires about 75% more energy than is eventually contained in the produced ethanol fuel.
Biodiesel is another proposed means for utilizing the renewable resources in the form of agricultural products. While this can be an effective means of using the oily component of the plant, there is only a small available yield of seed oils. It is estimated that if biodiesel fuels were to replace today's oil consumption, it would require 3.0 billion cultivated acres. Also, since only a small portion of the plant is used, this does not present an effective means of utilizing the fibrous component of biomass.
Yields from energy farming currently in place will not be sufficient for estimated national energy consumption unless means are provided to utilize the whole plant for energy production. The average biomass contains in dry mass at least 4,500 kilocalories per kilogram, and this energy content is comparable to many sub-bituminous coals, i.e., brown coals. However, unlike brown coal, the biomass source is an entirely renewable resource, contributing no new carbon dioxide, and its sulfur content is only a very small fraction of that found in coal.